Hi. It’s Mr. Andersen and in
this podcast I’m going to talk about plant structure. So a good way to think about this
is plant anatomy. If you never stood next to a giant sequoia then you should. It dwarfs
all the trees around iy. And it shows you how huge plants can become. Just using a few
simple ingredients like water, carbon dioxide and a few nutrients from the soil it can become
massive. And you can see the rings that we’ll talk about kind of near the end. And so basically
everything I’m going to talk about for the most part is going to be angiosperms. So flowering
plants. And flowering plants can be broken down into two different dicots and monocots.
And so what is a cot? A cot is simply a cotyledon. And so a cotyledon is going to be a baby plant
leaf. And so here we’ve got two different seed types. There’s going to be a seed coat
around the outside. And little endosperm in here. But you can see this baby plant. And
in this dicot you’ll have two cotyledons. One, two. But in a monocot you’re only going
to have one. Now the quintessential dicot that I think of is dandelion. And a monocot
I think about is grass. And so if you’ve ever looked at a dandelion leaf, all the veins,
which really are vascular material, it’s kind of like our circulatory system, moving water
and sugar, are going to be net like. They’re going to branch out. But if we’re talking
about a monocot, they’re going to be parallel. So if you’ve ever looked at the veins in the
grass, a blade of grass, it’s going to be all parallel. If you were to look at their
flowers, in a dicot, they’re going to have 4 to 5 or multiples of 4 to 5 on their petals.
So you can see 1, 2, 3, 4, 5. So probably a dicot. Where as if it’s a monocot, they’re
going to be in multiples of 3. So you can see that this one has 6 petals. And so it’s
going to be a monocot. And then another way to differentiate between the two is going
to be roots. A dandelion, if you’ve ever tried to pull one out, they have this really big
tap root system. But in monocots, like grass, they’re going to have a netlike root system.
And it’s going to be what makes up sod for example and grass. And so those are the different
types of angiosperms. When we talk about phytotomy you should realize that plants live a double
life. They live life underground. We call that the root system. And then they have a
life above ground. We call that the shoot system. Within that shoot system, basically
you’re going to have nodes. So that would be a node there. A node there. You could have
another node there. And another node up here. But the distance between those nodes is going
to be the internodes. So that would be the internode between the two. And so basically
plants are able to grow up, but they’re also able to grow out and each of these node points.
Just like use they’re going to have tissues. And so in us if we’re talking about tissues,
now you would think of muscular, excuse me, muscular nervous, connective and then epithelial.
But in plants there are just going to be three types of tissues. They have dermal tissue,
ground tissue and then vascular tissue. And just like us they break that into specific
types of cells. We’ve got the epidermis, which is the dermal lining. And then we have periderm,
which is going to be mostly when we get to the level of bark. So it’s secondary growth.
Function of that is to provide protection. So this is a cross-section of a leaf. So it’s
going to provide protection from the outside. Same thing right here. You can see this in
a stem. We’re going to have dermal tissues on the outside. And they also prevent water
loss. So basically epidermis is the big type of dermal tissue. Ground tissue is going to
be just run of the mill cells. And so this is going to be broken into three types. And
these words are really fun to say. Parenchyma, collenchyma, and sclerenchyma. What do they
do? Basically they do the jobs of the plant. So they’re going to be the site of photosynthesis
for example in the leaf. But it’s going to be metabolism, storage, growth. All of that
is going to be in the ground tissue. And then finally we have the vascular tissue. That’s
made up of two type. Xylem and phloem. And they’re going to move the water and the sugar.
So we’ll get more specific to each of these. So let’s start with the dermal tissue. Dermal
tissue, for the most part is going to be epidermis. So right here we’re looking at a cross-section
of a leaf. So this would be dermal tissue on the top and on the bottom. The guard cells
also make up part of that. And the guard cells, you can see a zoomed in version of it right
here. Basically what they do is they surround the stomata, or this opening. What does the
stomata do? You can see it’s the hole in the leaf. Basically it allows water to evaporate
out and that water as it evaporates out is going to carry water all the way up in the
plant. But they also bring in a really important gas. That’s going to be CO2. And so plants
kind of have guard cells that are doing really good feedback. Basically if they have a lot
of moisture and they can let a lot of it go and it’s really sunny they open the guard
cells up. And the stomata are going to allow a lot of water to come out, a bunch of carbon
dioxide in. And so they can make a bunch of sugars. Likewise if it’s really, really hot,
really, really dry, they can close up the stomata. So they don’t lose all of their water.
One thing that I should mention is going to be this real waxy covering on the epidermis.
That’s called the cuticle. And it’s like wax. It’s that wax that you feel, that slippery
stuff you feel on the outside of a leaf. And that’s going to prevent water from getting
in and getting out. If we get to the ground tissue, basic run of the mill cells are going
to be parenchyma cells. The typical plant cell is parenchyma cell. What do they do?
They’re going to be the site of metabolism. Site of photosynthesis. Outside that, as a
plant starts to grow we have the collenchyma. I always remember the c and l and collenchyma
stands for celery. So those are going to be these real durable cells on the outside of
celery. They provide support as it starts to grow. And so you can see the dermis on
the outside. Collenchyma cells. And then these are going to be parenchyma cells right here.
They provide support. And if you take a plant as it grows, and just mess with it all the
time, push it all the time, simulating like wind, the collenchyma gets stronger and stronger
and stronger. But it never gets as strong as the sclerenchyma. Sclerenchyma are going
to be the really durable, wooded kind of portions of a plant as it start to grow. This is a
sclerenchyma fiber that’s cut in half. If we were to look at a fiber we could find this.
This is hemp. We pulled the sclerenchyma cells out to use these fibers to make rope. It’s
incredibly durable. And so sclerenchyma is going to be these big fibers that give it
that really really strong, like in a branch that grows. But we’ll also have sclerenchyma
cells like the core of an apple, of example is sclerenchyma. It’s protecting the seeds
on the inside. Or the grit on the inside or a pear is sclerenchyma. So that’s the ground.
Now we go to the vascular. Vascular is going to be made up of two types. The xylem and
the phloem. So in this we’re cutting a stem apart. This would all be xylem in here. And
then level 4 right here is going to be phloem. Basically xylem is moving water. It’s going
to move water from the roots to the shoots. Phloem is going to move sugar up and down
in a plant. And so on the outside we’d have dermis. They we’re going to have so sclerenchyma
cells that are are giving it durable support. So now we’re going to talk about growth and
then finally finish up with flowers. But this is an old story. If you go and take a spike
and hammer it into a tree. Let’s say that we put it at about 3 feet right here. And
you come back in 100 years. So let’s say, make it more realistic, 40 years. And the
plant, the tree now, instead of being whatever, 16 feet tall is 160 feet tall. How high is
that spike going to be? Well the right answer is that it will still be 3 feet tall. Because
plants grow from the top and they grow from the bottom. They from from the shoots and
and the roots. But the middle is going to stay the same. Now the bark is going to start
to grow up. And so that tree might, the spike might not be as far in, but just like humans
we first grow up. Get much, much longer. And they we’re going to, I’ll tell you this, as
you get older you start to get wider and wider and wider. And so we call this primary growth.
This first growth. And how does that occur? Well we use something called an apical meristem.
Basically that’s going to be a site. Right here we’re looking at a root where you have
cells that keep copying themselves. We call those undifferentiated. Think of it like a
stem cell that keeps making copies of itself. And so that’s going to make new cells. And
as those cells get longer. As they mature and get larger and larger and larger, that’s
going to push this stem or root in this direction. Now I can tell this right here is going to
be a RAM or a root apical meristem because it has this root cap on the top of it. And
that root cap is going to allow it to push through the soil to find water. And so the
meristem is actually going to produce new cells on this side. Which will make the root
cap. And then cells on this side that make this root itself. If we look up at the SAM
or the shoot apical meristem, it’s not going to have this root cap. Because it’s doesn’t
have to, it’s just pushing it’s way through air. So it’s not going to have this. But it’s
still going to have this meristem. Because it’s producing new cells behind it. And as
they mature, it gets bigger and bigger and bigger. So that’s going to allow us to grow
up and down. But we also have secondary growth. Secondary growth allows us to get wider. And
so secondary growth, think about wooded growth. And so we’re looking at a tree now in this
diagram that has been sliced in half. And we’re zooming in kind of to the bark portion.
And so basically what you have is xylem. So xylem is going to be here on the inside. So
let’s put an X for the xylem. And then you’re going to have phloem here. And so what’s creating
the xylem and the phloem. This layer called vascular cambium. So what it’s doing is producing
new xylem here and it’s prodding phloem on this side. The phloem remember moves the sugar
and the xylem is going to move the water. So we’ve got xylem, vascular cambium, phloem.
As we move up you have a layer called the feloderm which isn’t found in all plants,
so let me cross that out. And then we have the cork cambium. The cork cambium is another
meristomatic layer. And that, just like the vascular cambium made phloem and xylem, cork
cambium is going to make this water proof cork on the outside. And so this guy right
here is peeling bark back from a tree. And so what is he exposing right here? He’s really
exposing the vascular cambium. He’s got xylem on the inside, phloem on the outside. And
so what he would really do if this is a tree that’s just standing, he would be girdling
the tree. He’d be killing the tree. Because if you remove that phloem and everything out,
then sugar can’t move up and down in a plant. You’d still have the xylem here, but without
sugar you can’t have life. And so one thing you know around here when you cut down a tree
is what you will get are theses rings. And so you see these rings. What are those rings?
Well the inside of a tree, wood for that matter, is going to be xylem. And so basically what
happens is it’s going to be wider when the cells are laid down during summer because
it’s growing really really quickly. But in the fall it’s going to be more dense. And
in the spring, because we can’t grow as quickly and not at all in the winter, and so you get
these seasonal rings. And so we can count them when it’s growing fast, slow, fast, slow.
And we can count the years, if we take a core sample. What would this look like in an area
where there is no seasons? It’s basically going to be uniform all the way out. Okay.
So that’s secondary growth. Last thing I want to finish with is the reproductive structure.
We call that the flower in angiosperms. Basically there’s the male part. That right here is
going to be the stamen. And then we’re going to have this, the female part. And so the
stamen right here is going to have on the head of it, we call this the anther. It’s
going to produce pollen grains. Those pollen grains are sperm essentially protected. So
those pollen grains, if they float away or are carried by a bee away, is going to be
the male reproductive structure. Female structure is going to be way down here inside the ovary
in this structure called the ovule. And so the egg is going to be protected right down
here. And then it’s surrounded by an ovary. Which will eventually ripen to form fruit.
But the way reproduction works in flowers is different than us. It’s just not sperm
meets egg. What we have is called double fertilization, which is kind of crazy but really, really
cool. So let’s say that the pollen lands right here. Basically what will happen is you’ll
get this pollen tube that will grow all the way out, all the way down here and it’s going
to grow into the ovule. Now within that pollen tube we’re going to have two sperm. And so
we’re going to zoom all the way down here into the ovule. So basically the pollen tube
is growing all the way down. And now we have these two sperm. So 1, 2 sperm. And those
are going to be those blue haploid structures right here. We have the egg, just like us.
This is exactly the same. We have egg and sperm, but we also have these polar nuclei
around the outside. So we have these two other nuclei. Each of those are haploid. And so
basically let’s look ahead. With fertilization one of the sperm fertilizes the egg. This
is going to make the new plant or the embryo. And then we’ve got the other sperm fertilizing
these two polar nuclei. And so this one is actually going to become triploid and this
one is going to become diploid. The diploid fertilized egg becomes the new plant. The
triploid fertilized polar nuclei becomes something called the endosperm. The endosperm is triploid.
Let’s zoom ahead to the seed. What does that look like? Well here’s going to be that triploid
endosperm. That’s going to be food for the plant. And the plant is going to be the embryo
right here. That’s diploid. And so basically when you plant a seed it’s protected by this
seed coat around the outside. This would be wheat seed. It’s protected by that. But when
it starts to germinate that embryo is going to start to grow. It’s going to start to become
the plant. But this endosperm is going to provide the food for that growing plant. As
it starts to grow, before it eventually starts to do photosynthesis and then the whole cycle
continues again. And so what have we talked about? Structure of plants. What’s going to
be in the next podcast? More of the physiology. How does this all work? How do we move nutrients
around in a plant. But for now I hope that’s helpful.